Kimbell-Diamond doctrine is a doctrine of income tax law. Under this doctrine, when a taxpayer who is interested primarily in a corporation's assets first purchases the stock and then liquidates the corporation in order to acquire the desired assets, the separate steps taken to accomplish the primary objective will be treated as a single transaction. Thus, even though the objective was accomplished in form by a purchase of stock, the substance of the transaction is a purchase of property. [United States v. Mattison, 273 F.2d 13, 17 (9th Cir. Idaho 1959)]

Kimbell-Diamond doctrine is otherwise known as the unitary transaction doctrine.